Electromechanical Transient Simulation Research Articles

Electromechanical Transient Modeling of the Low-Frequency AC System With Modular Multilevel Matrix Converter Stations

This paper studies the electromechanical transient modeling of a low-frequency AC (LFAC) system with modular multilevel matrix converter (M3C) stations. Firstly, the mathematical model of the M3C and its equivalent circuits are established. Then, an iterative power flow calculation algorithm for AC systems integrated with the M3C-LFAC system is developed. The dynamic model of the M3C for electromechanical transient simulation is studied and implemented in PSS/E. Based on a test system consisting of two asynchronous AC systems with an embedded M3C-LFAC system, comparisons between the electromechanical transient simulation results from PSS/E and the electromagnetic transient simulation results from PSCAD are conducted. The results from PSS/E and PSCAD coincide with each other well, and the validity of the established electromechanical transient model is proved. Lastly, a stability study of a modified New England 39-bus system with an embedded M3C-LFAC system is executed, and the characteristics of the M3C-LFAC system are presented.

Coordination of Multiple Flexible Resources Considering Virtual Power Plants and Emergency Frequency Control

High-voltage direct current (HVDC) blocking disturbance leads to large power losses in the receiving-end power grid, and the event-driven emergency frequency control (EFC) is an important measure to prevent large frequency deviation. By aggregating controllable distributed energy resources (DERs) on the demand side, a virtual power plant (VPP) could quickly reduce its power and can be a new fast response resource for EFC. Considering both the VPP and the traditional control resources, this paper proposes an optimized EFC strategy coordinating multiple resources for the receiving-end power grid with multi-infeed HVDC. The approximate aggregation model of the VPP response process is constructed, based on which the EFC strategy, aiming at minimizing the total control cost while meeting constraints on rotor angle stability and frequency deviation security, is proposed. The electromechanical transient simulation combined with particle swarm optimization (PSO) is utilized to solve the model, and parallel computation is utilized to accelerate the solving process. The effectiveness of the proposed EFC strategy is verified by a provincial receiving-end power grid with multi-infeed HVDC. The detailed simulation results show that VPP could dramatically reduce the control cost of EFC while maintaining the same stability margin.

Equivalent of distribution network with distributed photovoltaics for electromechanical transient study based on user-defined modeling

As more and more distributed photovoltaics (PVs) are installed in distribution networks, the dynamic characteristics of PVs affect the operation of the bulk power system. Accurate simulation of PV characteristics is essential for the needs of power system transient security and stability analysis. However, because of the large number of distributed PVs, detailed modeling of each PV significantly increases the electromechanical transient simulation time. The equivalent study of distribution networks with distributed PVs is needed to improve simulation efficiency. However, existing equivalent methods of PVs mainly focus on centralized PVs but are unsuitable for distributed PVs with significantly different dynamic characteristics. To improve simulation efficiency, this paper proposes an equivalent method of the distribution network with distributed PVs for electromechanical transient study based on user-defined (UD) modeling. Firstly, the equivalent structure of the distribution network is established. The static equivalent of the transmission lines and the dynamic equivalent model of loads are carried out. Then, a UD model based on PSASP is established for the dynamic equivalent of the distributed PVs. Compared with the current PV models in simulation software, the UD model has multiple sets of parameters for the equivalent of distributed PVs with different dynamic characteristics. Finally, the particle swarm optimization (PSO) algorithm is used to obtain the parameters of the equivalent PV. The effectiveness of the proposed method is verified under an example of a distribution network with PVs in PSASP.

Electromechanical transient simulation model of low frequency flexible transmission system based on modular multilevel matrix converter

Low frequency AC transmission has broad prospects in the future power system. How to establish its electromechanical transient simulation model and provide basic research means for its adaptability analysis after connecting to the large power grid is an urgent problem to be solved. Based on the existing electromechanical transient simulation methods, the mathematical model of modular multilevel matrix converter (M3C) is simplified, and an electromechanical transient simulation model composed of virtual DC circuit and equivalent AC circuit is proposed. On this basis, the power and voltage controller is designed according to the power decoupling characteristics of M3C. Further considering the operation requirements of the offshore wind power transmission system through low frequency AC transmission, an island control is designed to make M3C have the ability of passive control. Numerical examples verify the effectiveness of the proposed simulation model, which can effectively respond to short-circuit faults and power loss. This model can better meet the calculation requirements of large power grid simulation.

Excitation control of variable speed pumped storage unit for electromechanical transient modeling

In this paper, a new excitation control of variable speed pumped storage unit (VSPS) for electromechanical transient modeling is presented. Compared with the traditional VSPS excitation control based on current source, the inner loop control of rotor current is retained. The new VSPS excitation control model considers the rotor flux dynamics and represents it as a second-order system. The effectiveness of the proposed excitation control model is verified by the comparison between electromagnetic transient simulation and electromechanical transient simulation. The electromechanical transient simulation of VSPS based on current source and VSPS based on voltage source is compared to verify the necessity of considering rotor flux dynamics. The proposed VSPS excitation control model reflects the characteristics of controllable voltage source and can provide more accurate reactive power and voltage simulation results in transient stability analysis.

A General Equivalent Modeling Method for DFIG Wind Farms Based on Data-Driven Modeling

To enhance the stable performance of wind farm (WF) equivalent models in uncertain operating scenarios, a model-data-driven equivalent modeling method for doubly-fed induction generator (DFIG)-based WFs is proposed. Firstly, the aggregation-based WF equivalent models and the equivalent methods for aggregated parameters are analyzed and compared. Two mechanism models are selected from the perspective of practicality and complementarity of simulation accuracy. Secondly, the simulation parameters are set through two sampling methods to construct a training database. Next, the whole fault process is divided into five phases, and the weight coefficient optimization model is established according to the data-driven idea to achieve the adaptive configuration of the weight. Finally, the electromechanical transient simulations of the power systems with a DFIG-based WF is carried out by using the MATLAB/Simulink platform. Compared with the detailed WF model, the simulation time of the WF equivalent proposed in this paper can be significantly reduced by about 87%, and simulation results show that the proposed method can effectively improve the adaptability of the WF equivalent model in different wind scenarios and voltage dips.

Research on the Amplitude–Phase Motion Equation for the Modeling of Wind Power System

The increasing penetration of wind power together with its high volatility could significantly impact the transient stability of the power grid. To quickly evaluate this impact, current engineering practice is primarily relying on time-domain simulation, which is computationally expensive despite that the results are more accurate. To solve this computational complexity issue, the amplitude–phase motion method is proposed to establish the electromechanical transient simulation model of the double-fed induction generator (DFIG) for wind energy. However, the traditional amplitude–phase motion equation (APME) suffers from the instability control from the abrupt change of terminal voltage induced by the system changes or flickers. To improve the transient stability of DFIG, this study firstly incorporates the q-axis current together with the amplitude change of terminal voltage into the phase error of the phase-locked loop (PLL). Then, the output phase of the terminal voltage of DFIG is highly combined with the q-axis current and the amplitude of terminal voltage to improve the internal control effect of the typical APME. The simulation results in the four-machine two-area power system with one wind farm demonstrate that the proposed method is able to maintain a stable operation of the wind farm and the power grid when experiencing a sharp disturbance of wind speed.

Parallel Simulation of The Electromechanical Transient Phenomena of Power System via Modern Software Development Technique

The simulation of power system electromechanical transient phenomena is highly dependent on the knowledge and model of special domain. For this reason, traditional parallelization of the simulation must be coupled with concrete algorithm and code. In this paper, a parallelized electromechanical transient simulation program is proposed based on the open-source simulation engine called InterPSS and general open object-oriented modelling framework. The correctness and effectiveness of this framework have been verified by a large-scale simulation case.

Dynamic Identification of Equivalent Parameters of Mathematical Models of Power Electrical Equipment of Electromechanical Power Systems

The article describes a method for dynamic identification of AC and DC hybrid power network parameters. The inaccuracy of the parameters of the electromechanical transient simulation model of the power system has caused the obvious difference between the simulation results and the actual measurement, which has restricted its online application. Over the years, the dynamic parameter identification technology based on field test and test has made great progress, but it is far from satisfactory and accurate. There is still a long research journey for the requirements of performance. The online identification method based on the actual dynamic parameters of the power system is a way to solve the problem. The article includes the main microprocessor modules for system parametric identification of load (SIP L) and an overhead power transmission line (SIP TL). The article will analyze the active electrical network and passive electrical network

Electromechanical Transient Modeling and LVRT Parameter Identification of Large Capacity Full Power Converter Wind Turbines Based on PSASP Program

Full power converter wind turbine is the main type of wind power, so the simulation calculation needs to establish accurate model parameters. This paper analyzes the model structure of PSASP program according to its low voltage ride through control and physical characteristics, and puts forward the parameter identification method of LVRT characteristics of full power converter wind turbine, and to use the LVRT data of 5. 5MW unit for parameter identification and simulation verification. This paper proposes that the electromechanical transient simulation can ignore the part of the generator model of the full power converter wind turbine, and simulates the grid side converter with the controlled current source. The main characteristics of LVRT are determined by the control system of the converter. In order to do the parameter identification, it is necessary to calculate and analyze the control characteristics of multiple measured data. First, determine the control mode, then determine the control parameters to complete the parameter identification. In this paper, the modeling conditions and model structure of the full power converter wind turbine are confirmed. The correlation between the parameters during the LVRT fault and the parameters during the LVRT recovery period and the LVRT characteristics is analyzed. In this paper, a parameter identification method is proposed to analyze the active current and reactive current during the LVRT fault, which has strong physical significance and operability. Based on the actual LVRT characteristics of 5. 5MW wind turbine, the parameter identification and simulation are carried out to verify the correctness of the method.

Simulation test and parameter optimization of fast cut back of large thermal power plant in the condition of synchronization of large-scale wind power

Fast cut back (FCB) is an important condition in power control of steam turbine generator unit, which is closely related to the flexibility, safety and stability of thermal power unit. In this paper, the traditional single reheat steam turbine model were optimized and improved by adding the key links such as medium pressure control valve and bypass, and further adding the once through boiler, bypass control system, FCB action signal, excitation system and other models. A thermal power unit model suitable for FCB large disturbance condition simulation was established. The simulation results verify the effectiveness of the model, and meet the requirements of power system electromechanical transient simulation and FCB simulation. And then, this paper improved the PSO (Particle Swarm Optimization) algorithm, and combined the advantages of each algorithm in the aspects of calculation difficulty, convergence speed, accuracy, ability to jump out of local optimum, etc., puts forward and verifies the GA-PSO (Genetic Algorithm-PSO) optimization method. Finally, considering the stability and regulation performance of the system, the GA-PSO optimization algorithm was used to obtain the optimal values of the system component parameters. The simulation results indicated that the characteristics of optimized system damping was improved, which enhanced the regulation performance and stability of the system.

Hybrid Simulation for Large-Scale AC/DC Power System by Serial Interaction Process

Electromechanical transient (EMT) and transient stability hybrid simulations can make full use of their fast-solving ability and high-precision computing ability to accurately simulate the dynamic characteristics of large-scale AC/DC systems. This paper selects the bus as the hybrid simulation interface bus in the AC system near the DC system, which can effectively improve the simulation accuracy of the AC/DC system interaction. At the interface bus, Norton equivalent and Thevenin equivalent are applied to the EMT simulation side and electromechanical transient simulation side, respectively. The three-phase simulation data and three-sequence component simulation data are extracted respectively, and the serial iteration method is used for hybrid simulation calculation. This paper takes Zhangbei multi terminal AC/DC system as an example, compares the hybrid simulation results with the EMT simulation results, and tries to verify the accuracy and effectiveness of the hybrid simulation method.

Caracterización y simulación de fenómenos dinámicos relacionados con la actuación de un horno de arco eléctrico conectado al sistema eléctrico de potencia de Ecuador

La operación de los hornos de arco eléctrico (EAF) causa variaciones en las variables eléctricas, como son: potencia activa, reactiva, voltaje y frecuencia. Estas variaciones se deben al funcionamiento propio del EAF que produce un consumo altamente intermitente, lo que lo hace una carga especial. Este trabajo presenta una metodología para el análisis e interpretación de los datos registrados por el sistema SCADA/EMS y el sistema de monitoreo de área extendida WAMS, durante la operación de un EAF conectado al sistema eléctrico de potencia (SEP) de Ecuador. El propósito de este análisis es caracterizar las perturbaciones a través de las variables eléctricas frecuencia, voltaje, potencia activa y reactiva, medidas en la Subestación más sensible a la operación del EAF. Para esto, se realiza un análisis de datos multivariantes basado en Funciones Empíricas Ortogonales EOF, junto con clasificadores inteligentes. Adicionalmente, se propone un modelo de EAF para simulación de transitorios electromecánicos, el cual se basa en un tren de pulsos de ancho modulado (Pulse-width modulation PWM), afectado por una señal de ruido de frecuencia parametrizable. Tanto la propuesta metodología para caracterización de la actuación del EAF a través de registros, como el modelo propuesto muestran prometedores resultados respecto de la evaluación post-operativa y de planeamiento operativo del impacto de la operación de un EAF en el SEP.

Research on agile generation method of electromagnetic transient simulation model based on multiple information sources

Based on electromechanical transient simulation data, an electromagnetic transient simulation model can be quickly generated through a computer program. However, electromechanical transient data are not sufficient to describe completely the corresponding electromagnetic transient simulation model. In view of this, the paper proposes an electromagnetic transient simulation model generation method that integrates multiple information sources. First, the data characteristics of electromechanical transient simulation software PSD-BPA and electromagnetic transient simulation software PSCAD/EMTDC are introduced. Then, considering the difference between electromechanical transient and electromagnetic transient model data, a method to quickly generate PSCAD/EMTDC simulation data is established. This method is based on the electromechanical transient simulation data, and takes into account those information which is not available in the electromechanical transient data but needed in the electromagnetic transient in the conversion process, so that the converted model is more detailed and accurate. Finally, this method is used to model and analyse an actual fault. The simulation results show that the method proposed in the paper is effective and credible.

Research on the Parameter Test and Identification Method of Electromechanical Transient Model for PV Power Generation

Model and parameters are the indispensable conditions for the simulation calculation of power systems with a high proportion of photovoltaic power generation. Conventional models of power electronic devices are difficult to meet the requirement of power system electromechanical transient simulation, and the parameters are difficult to obtain. Aiming at this problem, this paper proposes a structure of an electromechanical transient simulation model of a photovoltaic power station and designs a set of photovoltaic power generation transient characteristic test systems based on a fault simulation device. Through a disturbance test and model parameter identification, the electromechanical transient simulation model and parameters of photovoltaic power generation are obtained. In this paper, based on the test system, the electromechanical transient characteristics of a certain type of photovoltaic inverter are modeled. The results show that the model can successfully describe the electromechanical transient characteristics of photovoltaic power generation, and the simulation results obtained based on the model parameters have a good fitting degree compared with the measured curve.

Analytical method to calculate transient responses of induction motor load

An analytical method to calculate the transient responses of induction motors (IMs) following power system symmetrical and asymmetrical voltage sags is developed based on circuit and machine analysis theory. The derived calculation models and algorithm are composed of a series of algebraic formulae. The slip, transient voltage, stator current, and electrical power of the perturbed IM can be computed. Compared with electromagnetic transient simulation results using the PSCAD/EMTDC software package, the accuracy of the proposed method is proved. Applying the proposed method to calculate the transient responses of power system IM composite load shows that the approach not only has the advantage in computing speed but also improve the accuracy of power system electromechanical transient time domain simulations under unbalanced faults caused voltage sag.

Behavioural mechanism and stability control of VSC–HVDC/weak AC hybrid grid after large disturbances

Flexible DC transmission technology based on voltage source converter (VSC) is an effective solution to solve the reliability of power supply to weak AC systems. In this study, a VSC-high-voltage DC (HVDC) electromechanical transient simulation model is established based on the Chongqing-Hubei flexible DC transmission project which is the highest voltage level and the largest transmission capacity in the world. This model can be used to simulate the behaviour of the limiters and AC fault ride through strategies. A large disturbance measurement method for VSC's non-linear power characteristics is proposed. Stability of flexible DC and weak AC hybrid grid under large disturbance are analysed, behaviour mechanisms and key influence factors of different instability forms are revealed. In this way, a solution is proposed to improve the hybrid grid's ability against large disturbances. By the construction of the VSC-HVDC electromechanical transient simulation model, the correctness of the mechanism analysis and effectiveness of the solution are verified.

Modeling and simulation of large power system with inclusion of bipolar MTDC grid

This paper presents an electromechanical transient modeling and simulation method for large power system with inclusion of bipolar multi-terminal direct current (MTDC) grid. First, the dynamic model of a modular multilevel converter (MMC) is presented. The dynamic model of the bipolar DC grid is then established by using the companion circuit method. In particular, the inductances of DC lines are carefully modeled to ensure the simulation accuracy when a DC fault occurs. Second, the electromechanical transient simulation procedure for a power system with inclusion of an MTDC grid is presented. The AC and DC grids are solved alternately. Due to the difference between time constants of AC and DC grids, the multi-rate scheme is used to ensure the simulation efficiency. Third, the proposed method is employed to simulate a real-life large power system with inclusion of a bipolar MTDC grid. The simulation results validate the correctness and the effectiveness of the proposed method. Unique interaction characteristics between AC and DC grids are also revealed by the results.

Research on simulation technology of power system operation and dispatch control based on trend tracking

Over the past decade, Chinese energy structure and power system technology have undergone tremendous changes. First, the proportion of new energy in power generation capacity is increasing, and the permeability of some areas has reached 30% - 50% of the total power generation capacity; second, the characteristic of power electronics in power system is becoming more and more obvious. The impact of these two aspects on the power system is that the power fluctuation of the power grid is intensified, and the power flow is flexible and changeable, which brings new challenges to the operation scheduling and simulation technology of the power system. Therefore, based on Power System Analysis Synthesis Program (PSASP) electromechanical transient simulation program, this paper studies and proposes a power grid regulation and control analysis method, it can help the dispatchers and operators to improve the dispatching plan and the accuracy of various kinds of anticipated faults. This method seeks to simulate the power flow fluctuation of the real power grid approximately. The validity of the proposed method is verified by the simulation calculation of some year national interconnection data.

Electromechanical Transient Modeling and Control Strategy of Decentralized Hybrid HVDC Systems

This paper studies the electromechanical transient model and the control strategy of line commutated converter (LCC) and modular multilevel converter (MMC) based decentralized hybrid High Voltage Direct Current (HVDC) Transmission systems. The decentralized hybrid HVDC system is a new type of topology, and the related electromechanical transient model and control strategy have not been studied well. In this paper, the electromechanical transient model of a decentralized hybrid HVDC system is devloped through mathematical deduction. This model can be easily implemented in electromechanical transient simulation software and meet the time domain simulation requirements of large-scale systems. Then, in order to ensure the safe absorption of the DC power under various conditions, an optimal power flow model considering the decentralized hybrid HVDC system is proposed. Finally, the electromechanical transient model proposed in this paper is verified by the electromagnetic transient model, and the control strategy is validated in a modified New England 39-bus system.